In a stereophonic sound reproduction setup comprising a left and a right loudspeaker radiating sound into a listening area in front of the loudspeakers, optimal stereophonic sound reproduction can be obtained in the symmetry plane between the two loudspeakers. Hence, if substantially identical signals are provided to the two loudspeakers, a listener sitting in front of the loudspeakers in the symmetry plane will perceive a sound image in the symmetry plane between the loudspeakers. However, if the listener for instance moves to the right relative to the symmetry plane, the distance between the listener and the right loudspeaker will decrease and the distance between the listener and the left loudspeaker will increase, resulting in that the perceived sound image will move in the direction of the right loudspeaker, even though identical signals are still applied to the two loudspeakers. Thus, generally, the perceived position of specific sound images in the total stereo image (for instance resembling a singer or a specific instrument in an orchestra) will depend on the lateral position of the listener relative to the loudspeaker setup. This effect is however not desirable, as a stable stereophonic sound image is desired, i.e. a sound image in which the position in space of each specific detail of the sound image, such as for instance the position of a singer, remains unchanged, when the listener moves laterally in front of the loudspeakers, as it would do, if the listener was listening to a real singer standing somewhere at a stage for instance surrounded by an orchestra. Consequently there is a need for a stereophonic loudspeaker setup that does not suffer from this disadvantageous effect of the position of the listener relative to the loudspeaker setup on the perceived sound image.
Furthermore, the directional characteristics of the loudspeaker units used in traditional stereophonic loudspeaker systems depend on frequency. At low frequencies a loudspeaker unit may have a substantially omnidirectional characteristic, radiating sound energy substantially equally in all directions. However, at mid frequencies and even more at high frequencies the directional characteristic tend to be more and more narrow, such that the loudspeaker unit predominantly radiates sound energy in a narrow beam in the direction of the loudspeaker symmetry axis. This may cause deteriorated sound reproduction for a listener positioned off-axis relative to the loudspeaker system. Hence, there is a need for a loudspeaker system with a directional characteristic with reduced dependency on frequency.